Of state. Contents and Concepts 1. Comparison of Gases, Liquids, and Solids Changes of State

Problem Strategy Note that above the critica temperature, a gas cannot be liquefied (that is, transformed so that the gas coexists in equilibrium with the liquid). This can occur only below the critical temperature.

Solution The critical temperature of ammonia is well above room temperature. If ammonia gas at room temperature is compressed, it will liquefy.

Nitrogen, however, has a critical temperature well below room temperature. It cannot be liquefied by compression unless the temperature is below the critical temperature.